Confined MOF pyrolysis within mesoporous SiO2 core–shell nanoreactors for superior activity and stability of electro-Fenton catalysts

Despite the high density and uniform distribution of active sites in metal–organic frameworks (MOFs) and their derivatives, the relatively low stability in water still limits their utilization in heterogeneous catalysis. Herein, the confinement of pyrolyzed MIL-88B(Fe) derivatives within mesoporous SiO2 allowed fabricating core–shell nanoreactors (Fe/C@mSiO2) that served as heterogeneous electro-Fenton (HEF) catalysts for the first time, revealing an excellent performance. The as-prepared catalysts were featured by high specific surface area and dense active sites. During service as core–shell nanoreactors, they behaved as a dual function adsorbent-catalyst, exhibiting superior catalytic activity and recyclability as compared to HEF catalysts without shell. Using 0.2 g/L of catalyst, the complete removal of bisphenol A at pH 6.2 and 100 mA was achieved at 120 min, with extremely low iron leaching of 0.11 mg/L. The rigid mSiO2 shell not only protected the iron active sites from leaching, but it also provided porous and permeable channels for efficient mass transport. The unique core–shell architecture concentrates the catalytic sites and reactants within a confined space, promoting the fast degradation of bisphenol A. Furthermore, the defect-rich carbon substrate and the high dispersibility of iron-rich sites favor a fast electron transfer. The efficient treatment of several organic micropollutants in consecutive trials corroborated the high activity and stability of the Fe/C@mSiO2. This work contributes to the rational design of HEF catalysts, aiming at consolidating their practical application in advanced wastewater treatment.